Understanding the dynamics of ongoing volcanic eruptions is essential for predicting the input and transport of volcanic ash in the atmosphere. To constrain near-vent dynamic processes of explosive Vulcanian events, we used Doppler radar measurements, providing tephra velocities and a proxy of the mass flux, in two field experiments at Volcán de Colima (Mexico) and Santiaguito (Guatemala). We find that explosive eruptions at both volcanoes consist of individual degassing pulses. The analysis of the timing of such pulses shows that both volcanoes have preferred interpulse times of 3 s (Santiaguito) and 2–5 s (Volcán de Colima). The interpulse time during one event may change, but it often returns to the preferred interpulse time. This behavior is similar at both volcanoes and the interpulse time roughly follows a log-logistic distribution indicating the interplay of two competing processes. These could be short-duration degassing of the uppermost conduit versus decreasing permeability due to progressive gas loss and compaction during an eruption.

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